1. Field of the Invention
This invention relates generally to the field of wireless data systems. More particularly, the invention relates to an apparatus and method for reducing power consumption in a wireless device.
2. Description of the Related Art
A variety of wireless data processing devices have been introduced over the past several years. These include wireless personal digital assistants (“PDAs”) such as the Palm® VIIx handheld, cellular phones equipped with data processing capabilities, and, more recently, corporate wireless messaging devices such as the Blackberry™ wireless pager developed by Research In Motion (“RIM”).™
Many of these wireless devices are capable of transmitting data (as well as audio signals) at two or more discrete power levels. The specific power level selected is generally directly related to the received signal strength indication (“RSSI”) at the device. Thus, referring to FIG. 1, as the received signal strength increases, the power level at which the device transmits decreases in a step-wise manner. For example, when the received signal strength is between 0 and RSS1, the wireless device transmits at its highest power level, P3. Similarly, when the received signal strength is above some maximum value, RSS2, the wireless device transmits at its lowest power level P1. This fixed relationship is based on the assumption that if the energy of the signal transmitted from the base station is relatively low, then the wireless device must be relatively far away from the base station and, therefore, must transmit at a relatively high power level for its signal to successfully reach the base station. Of course, variables other than distance between the device and the base station may affect signal strength. However, the assumption is that these variables will affect the transmitted signal and the received signal equally.
One problem which exists with the foregoing configuration is that devices are incapable of deviating from the direct relationship between RSSI and the transmission power level. Accordingly, once a device selects a particular power level at which to transmit based on RSSI, it does not increase its power level in the event of a series of unsuccessful transmissions. It also does not decrease the power level in the event that selected power level is unnecessarily high.
Many wireless devices are also capable of entering a low power mode (commonly referred to as a “sleep” or “standby” mode) in which they consume substantially less power than during normal operation, thereby prolonging battery life. However, these power management techniques are overly simplistic and inefficient in certain circumstances. For example, in wireless device with dual processors (e.g., a baseband processor and a CPU), prior power management techniques do not allow each processor to be powered down independently of one another.
Accordingly, what is needed is a more efficient and flexible power selection scheme. What is also needed is a more intelligent, efficient power management system whereby selected logical portions of the wireless device (e.g., a single processor in a dual processor system) can operate at a low power level while the remaining logical portions operate at a standard power level. What is also needed is a power management system which is backwards-compatible with current power management protocols (e.g., Mobitex).